1. Field of the Invention
The present invention relates to a method and an apparatus for detecting the number of persons in a particular place such as in a building, in an underground mall or a like place by processing picture signals from a TV camera.
2. Description of the Prior Art
A method has been widely employed according to which video signals of a TV camera are converted into digital signals, and a picture to be detected is recognized from the thus obtained digital signals. FIG. 3 is a block diagram showing a conventional apparatus for detecting the number of persons, wherein reference numeral 1 denotes a picture input unit which consists of a TV camera or the like and which takes a picture of persons to be detected and produces picture signals, reference numeral 2 denotes a preprocessing unit which receives picture signals from the picture input unit 1, removes noise components, converts them into binary signals and produces binary picture signals, 3 denotes an object pick-up unit which receives picture signals from the preprocessing unit 2 and picks up a picture of persons to be detected, 4 denotes an area comparator unit which compares the picture of persons picked up by the object pick-up unit 3 with a reference area picture that has been input and stored therein in advance, and reference numeral 5 denotes a counter unit which counts a picture that is greater than the reference area picture.
The operation will now be described. The picture input unit 1 takes a picture of a particular place such as in a building or in an underground mall and produces picture signals. The preprocessing unit 2 receives the picture signals, removes noise components through masking, and converts them into binary picture signals. The object pick-up unit 3 picks up a picture of persons to be detected from the binary picture signals. The area comparator unit 4 compares a reference area picture which has been stored therein in advance with the picture of persons to be detected picked up by the object pick-up unit 3, in order to obtain pictures of persons of portions greater than the reference area picture. The counter unit 5 counts these pictures and produces number-of-persons signals.
As mentioned above, the picture signals from the picture input unit are digitized in order to detect the number of persons to be detected.
According to the above-mentioned conventional apparatus for detecting the number of persons which determines the areas based upon the binary picture signals, however, the picture area (number of pixels or picture elements) of persons to be detected becomes so small as to make the detection difficult when the contrast over the background is small, such as when the hair is blond and the background floor has similar color. Due to a change in the intensity of illumination in a place where the picture input unit is installed, furthermore, it is difficult to set a threshold value when the signals are to be converted into binary signals. When the persons to be detected are imaged by the TV camera hanged from the ceiling, furthermore, the picture area becomes small at the center and becomes great toward the periphery to deteriorate the accuracy of detection. Moreover, when the picture signals are digitized to detect the number of persons, a problem arises with regard to the processing time; i.e., the processing becomes longer with an increase in the degree of processing.